A crystal oscillator is referred to as a crystal, and is a type of high-precision and high-stability oscillator. In electronic circuit applications, it can cooperate with other components to generate a standard pulse signal with specific oscillation frequency as a clock signal or to provide a reference signal for a specific system.
For the crystal oscillator circuit, too-long start-up time is one of the ever-present problems. From the view point of magnitude, the low-frequency crystal oscillator circuit takes about several hundred milliseconds or a few seconds of the start-up time to start, which is far slower than the high-frequency crystal oscillator circuit. In the crystal oscillator circuit, one of the factors causing a long start-up time may be the low loop-gain of the crystal oscillator circuit.
FIG. 1 is an existing crystal oscillator circuit. As shown in FIG. 1, the existing crystal oscillator circuit 100 is a type of crystal oscillator circuit with low-power consumption, and includes: an oscillator start-up circuit (not labeled) containing a crystal oscillator XTAL, a first load capacitor C1, a second load capacitor C2, and an inverter INV. A first output terminal and a second output terminal of the crystal oscillator XTAL are respectively connected to a first output terminal and a second output terminal of the oscillator start-up circuit. A first terminal of the first load capacitor C1 is connected to the first output terminal of the oscillator start-up circuit, and a second terminal of the first load capacitor C1 is grounded.
A first terminal of the second load capacitor C2 is connected to the second output terminal of the oscillator start-up circuit, and a second terminal of the second load capacitor C2 is grounded. An input terminal and an output terminal of the inverter INV are respectively connected to the first output terminal and the second output terminal of the oscillator start-up circuit. The crystal oscillator circuit 100 also includes a first current source I1 for outputting a first current to drive the oscillator start-up circuit. Further, the crystal oscillator circuit 100 includes a cascade of at least one buffer (BUF, FIG. 1 only illustrates one BUF) for converting a first oscillation signal to a rectangular wave signal and outputting the rectangular wave signal.
However, such crystal oscillator circuit 100 often faces an issue of too-long start-up time. The disclosed device structures and methods are directed to solve one or more problems set forth above and other problems.